Aquatic and Wetland Vascular Plants of the Northern Great Plains

15. Polygonaceae, the Smartweed Family

1. Polygonum L. -- Smartweed, knotweed, tear-thumb

2. Polygonum bicorne Raf.-- Pink smartweed

Very similar to P. pensylvanicum and often included in it by authors.
Differing in having heterostylic flowers which are consistently pink; racemes
appearing fringed due to the extruded stamens and styles, some flowers with
the stamens exserted from the perianth and the styles included, others with
the stamens included and the styles exserted; calyx 3-4 mm long, conspicuously
exceeding the achene. Achenes lenticular, concave on both sides and usually
with a slight elevation in the center of the concavity. Jul--Sep. Shores, stream
banks, ditches and other wet, disturbed habitats; occasional in se SD, c and
e NE; (IL to SD and e CO, s to LA, TX and into Mex.). P. longistylum
Small.